Typhoid (or typhoid fever) is a serious bacterial infection that spreads through contaminated food and water. The disease causes high fever, weakness, stomach pain, and headaches that can last for weeks. Before modern medicine, typhoid killed thousands of people every year.

The bacteria that cause typhoid live in human waste, so the disease spreads when sewage contaminates drinking water or when infected people handle food without washing their hands properly. This made typhoid especially dangerous in crowded cities before the development of modern plumbing and water treatment systems. Today, typhoid remains a problem in places without clean water and good sanitation, though vaccines and antibiotics can prevent and treat it.

A famous case in American history involved Mary Mallon, known as Typhoid Mary, a cook in New York City in the early 1900s. She carried the disease without getting sick herself and unknowingly infected dozens of people. Her story helped scientists understand that healthy people could spread diseases, which changed how we think about public health. The name Typhoid Mary is now sometimes used to describe anyone who spreads problems without meaning to, though this usage can be unfair and unkind.